U.S. patent number 9,333,953 [Application Number 14/430,233] was granted by the patent office on 2016-05-10 for electric parking brake system.
This patent grant is currently assigned to NTN CORPORATION. The grantee listed for this patent is Yui Masuda, Makoto Muramatsu. Invention is credited to Yui Masuda, Makoto Muramatsu.
United States Patent |
9,333,953 |
Masuda , et al. |
May 10, 2016 |
Electric parking brake system
Abstract
An electric parking brake system includes an electric motor; a
linear motion mechanism that converts the rotational movement of a
rotor shaft of the electric motor to a linear movement of a slide
member to operate a brake; a locking mechanism that fixes a
position of the slide member; a control device that controls the
electric motor and the locking mechanism; a brake load estimation
unit that estimates a brake force; and an electric parking brake
operation instruction device that is arbitrary operable. The
control device automatically executes a parking brake operation
when a stop state of the vehicle is detected even if the electric
parking brake operation instruction device is not operated. The
automatically applied parking brake force is set to a value smaller
than the normal parking brake force applied by the parking brake
operation instruction device.
Inventors: |
Masuda; Yui (Shizuoka,
JP), Muramatsu; Makoto (Shizuoka, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Masuda; Yui
Muramatsu; Makoto |
Shizuoka
Shizuoka |
N/A
N/A |
JP
JP |
|
|
Assignee: |
NTN CORPORATION (Osaka,
JP)
|
Family
ID: |
50477481 |
Appl.
No.: |
14/430,233 |
Filed: |
October 10, 2013 |
PCT
Filed: |
October 10, 2013 |
PCT No.: |
PCT/JP2013/077598 |
371(c)(1),(2),(4) Date: |
March 23, 2015 |
PCT
Pub. No.: |
WO2014/058015 |
PCT
Pub. Date: |
April 17, 2014 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150246662 A1 |
Sep 3, 2015 |
|
Foreign Application Priority Data
|
|
|
|
|
Oct 12, 2012 [JP] |
|
|
2012-226702 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60T
7/12 (20130101); B60T 7/107 (20130101); F16D
65/18 (20130101); B60T 8/172 (20130101); B60T
13/741 (20130101); B60T 7/085 (20130101); F16D
2121/24 (20130101); F16D 2125/40 (20130101); F16D
2125/50 (20130101); F16D 2125/48 (20130101) |
Current International
Class: |
G06F
7/70 (20060101); B60T 7/10 (20060101); B60T
13/74 (20060101); B60T 7/12 (20060101); B60T
7/08 (20060101); F16D 65/18 (20060101); B60T
8/172 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2 433 843 |
|
Mar 2012 |
|
EP |
|
11-147458 |
|
Jun 1999 |
|
JP |
|
2006-183809 |
|
Jul 2006 |
|
JP |
|
2007-015602 |
|
Jan 2007 |
|
JP |
|
2010-065777 |
|
Mar 2010 |
|
JP |
|
2010-090959 |
|
Apr 2010 |
|
JP |
|
2010-269671 |
|
Dec 2010 |
|
JP |
|
2012-087889 |
|
May 2012 |
|
JP |
|
Other References
International Search Report issued Jan. 7, 2014 in International
(PCT) Application No. PCT/JP2013/077598. cited by applicant .
Written Opinion of the International Searching Authority issued
Jan. 7, 2014 in International (PCT) Application No.
PCT/JP2013/077598 (with English translation). cited by
applicant.
|
Primary Examiner: Cheung; Calvin
Attorney, Agent or Firm: Wenderoth, Lind & Ponack,
L.L.P.
Claims
The invention claimed is:
1. An electric parking brake system comprising: an electric motor;
a linear motion mechanism that converts a rotational movement of a
rotor shaft of the electric motor to a linear movement of a slide
member to operate a brake; a locking mechanism that fixes a
position of the slide member; a control device that controls the
electric motor and the locking mechanism; a brake load estimation
unit that estimates an actually acting braking force; and an
electric parking brake operation instruction device that is
arbitrary operable; wherein the control device automatically
executes a parking brake operation when a stop state of the vehicle
is detected even if the electric parking brake operation
instruction device is not operated; and an automatically applied
parking brake force at time of the parking brake operation executed
when the stop state is detected is set to a value smaller than a
normal parking brake force at time of normal parking brake
operation by the operation of the parking brake operation
instruction device.
2. The electric parking brake system according to claim 1, wherein
the control device comprises an automatically applied braking force
determination unit that determines the automatically applied
parking brake force, the automatically applied braking force
determination unit having a function of determining the
automatically applied parking brake force so as to be equal to a
braking force by a service brake estimated by the brake load
estimation unit when the stop state of the vehicle is detected.
3. The electric parking brake system according to claim 2, wherein
the control device further comprises an inclination angle detection
unit that detects an inclination angle of the vehicle in a front
and back direction of the vehicle while the vehicle is at a stop,
and a frictional force estimation unit that estimates a frictional
force of the brake by the service brake while the vehicle is at a
stop; and the automatically applied braking force determination
unit is configured to calculate an estimated value of a braking
force necessary for maintaining a stop state of the vehicle from
the inclination angle obtained by the inclination angle detection
unit and the frictional force obtained by the frictional force
estimation unit, and determine the automatically applied parking
brake force from the estimated value.
4. The electric parking brake system according to claim 1, wherein
the control device is configured to stop power supply to the
electric motor when the parking brake operation executed when a
stop state of the vehicle is detected is completed.
5. The electric parking brake system according to claim 1, wherein
the control device is configured to release the parking brake
operation when a depressing force applied to a brake pedal becomes
smaller than a predetermined threshold value.
6. The electric parking brake system according to claim 1, wherein
the parking brake operation is released when a differential value
of a depressing force applied to a brake pedal becomes smaller than
a predetermined threshold value.
7. The electric parking brake system according to claim 1, wherein
the control device comprises a driving force detection unit that
detects a driving force acting on a drive wheel of the vehicle; the
control device is configured to calculate a necessary driving force
necessary to prevent the vehicle from at least moving backward,
from the inclination angle obtained by the inclination angle
detection unit, the driving force obtained by the driving force
detection unit, and information on a weight of the vehicle, when
the vehicle is inclined such that gravity acts on the vehicle in an
opposite direction with respect to an advancing direction of the
vehicle, and set a delay time for delaying the release of the
parking brake operation until the driving force reaches the
necessary drive force.
8. The electric parking brake system according to claim 1, further
comprising a gear reduction mechanism provided between the electric
motor and the linear motion mechanism and configured to reduce the
speed of, and output, the rotation of the rotor shaft of the
electric motor; wherein the locking mechanism comprises a locking
portion provided on a side surface of one of a plurality of gears
forming the gear reduction mechanism, a locking pin configured to
be moved forward and backward with respect to the locking portion
and brought into engagement with the locking portion to lock the
rotation of the gears when the locking pin is moved forward, and a
pin driving actuator configured to move the locking pin forward and
backward; and the position of the slide member is fixed and the
fixing is released by the locking and unlocking of the gears by the
locking pin.
Description
TECHNICAL FIELD
The present invention relates to an electric linear motion actuator
that linearly drives a driven member such as a brake pad, and an
electric brake system that uses the electric linear motion
actuator.
BACKGROUND ART
In an electric linear motion actuator having an electric motor as a
drive source, the rotational movement of a rotor shaft of the
electric motor is converted to a linear movement of an axially
movable driven member by a motion converting mechanism.
A ball screw mechanism and a ball ramp mechanism are known for the
motion converting mechanism adopted in the electric linear motion
actuator. Although such motion converting mechanism has a force
multiplying function to a certain extent, a large force multiplying
function required in the electric disc brake system, and the like
cannot be ensured.
Thus, in the electric linear motion actuator adopting the motion
converting mechanism described above, the drive force is increased
by separately incorporating a speed-reducing mechanism such as a
planetary gear mechanism, whereby the configuration becomes complex
and the electric linear motion actuator enlarges by the
incorporation of the speed-reducing mechanism.
In order to solve such problems, the applicant of the present
application has already proposed, in the below-identified patent
document 1 and patent document 2, an electric linear motion
actuator that can ensure a large force multiplying function without
incorporating the speed-reducing mechanism and that is suited for
use in the electric disc brake system in which a linear stroke is
relatively small.
In the electric linear motion actuator described in patent document
1 and patent document 2, planetary rollers are mounted between a
rotation shaft, which is rotation driven by an electric motor, and
an axially movable outer ring member. When the rotation shaft is
rotated, the planetary rollers are revolved while spinning by
frictional contact with the rotation shaft, and the outer ring
member is axially moved due to engagement of a helical rib formed
on the radially inner surface of the outer ring member in a helical
groove or circumferential grooves formed in the radially outer
surface of each planetary roller.
In the electric disc brake system adopting the electric linear
motion actuator described in patent document 1 and patent document
2, only a service brake function that controls the braking force in
accordance with the operation of the brake pedal of the driver is
provided, and hence the electric motor needs to be kept energized
to maintain the braking force at the time of parking, which is
extremely disadvantageous in terms of power consumption.
A great effect can be obtained in resolving the disadvantages
described above by adding a parking brake locking mechanism by a
solenoid and regulating the rotation of the rotor of the electric
motor in the brake-releasing direction by the actuation of the
parking brake locking mechanism as in an electric brake system
described in patent document 3.
However, in the electric brake system described in patent document
3, although the parking brake locking mechanism is arranged, such
parking brake locking mechanism is arranged at a periphery of the
rotor and hence the radial dimension becomes large and the parking
brake locking mechanism may interfere with the wheel when assembled
to a vehicle. Furthermore, since the parking brake locking
mechanism is arranged at the periphery of the rotor, the weight on
the electric motor side becomes heavy thus causing the weight
balance to degrade. Such degradation in the weight balance
adversely affects the contact of the brake pad at the time of
braking, whereby the braking becomes unstable and a brake noise may
generate.
The electric brake system described in patent document 4, a locking
mechanism for locking and unlocking the rotation of the rotor shaft
of the electric motor includes a plurality of locking portions
arranged in the circumferential direction of a side surface of one
of a plurality of gears forming a gear reduction mechanism, a
locking pin that can move forward and backward with respect to the
locking portions, and a pin driving actuator that moves the locking
pin forward and backward. The locking pin and the pin driving
actuator are incorporated between the electric motor and a housing
that houses a slide member and a rotation/linear movement
converting mechanism, whereby the electric disc brake system that
is small and compact and that excels in weight balance is
realized.
PRIOR ART REFERENCES
Patent Documents
Patent document 1: Japanese Laid-Open Patent Publication No.
2010-65777
Patent document 2: Japanese Laid-Open Patent Publication No.
2010-90959
Patent document 3: Japanese Laid-Open Patent Publication No.
2006-183809
Patent document 4: Japanese Laid-Open Patent Publication No.
2012-087889
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
In an electronically controllable electric parking brake system of
the brake-by-wire configuration, in which the brake pedal is
connected to the actuator by an electric cable (wire) by way of a
computer, and a friction brake is actuated by the actuator, if this
system is configured such that parking brake can be automatically
applied, it is unnecessary to keep depressing the brake pedal while
the vehicle is at a stop. Also, if such a parking brake system is
used to assist in e.g. hill start, it will improve safety of the
vehicle.
Moreover, when driving the service brake (regular brake) with the
electric motor, it is also effective to utilize the operation of
the electric parking brake system as a measure for reducing the
loss by the motor current when continuously exerting the brake
force.
When actively performing the control of the electric parking brake
system, however, a rapid lock-and-release operation of the parking
brake is necessary to prevent the vehicle driver from feeling a
sense of discomfort.
This is because the braking force used in the normal parking brake
is generally the same as or greater than the maximum braking force
of the service brake, and thus the response speed of the parking
brake operation (lock-and-release operation) by such parking brake
system tends to be slow. In other words, such electric parking
brake operation can hardly be used for purposes other than for
normal parking brake operation initiated by the driver.
Furthermore, if the braking force of the normal parking brake is
repeatedly used, the demand for durability on the component parts
of the brake may become high, which may result in increased cost
and weight.
It is an object of the present invention to extend the application
range of the parking brake operation by the electric parking brake
system.
Means for Solving the Problems
In order to solve the problem described above, according to the
present invention, the electric parking brake system is controlled
such that parking brake operation is carried out automatically
without depending on the operation of a vehicle driver when the
vehicle is brought to a stop, and the parking brake force generated
by the parking brake operation is close to the braking force of the
service brake (regular brake) used for stopping the vehicle.
In a specific arrangement, the present invention provides an
electric parking brake system comprising: an electric motor; a
linear motion mechanism that converts the rotational movement of
the rotor shaft of the electric motor to a linear movement of a
slide member to operate a brake; a locking mechanism that fixes the
position of the slide member; a control device that controls the
electric motor and the locking mechanism; a brake load estimation
means that estimates the actually acting braking force; and an
electric parking brake operation instruction device that is
arbitrary operable; wherein the control device automatically
executes a parking brake operation when a stop state of the vehicle
is detected even if the electric parking brake operation
instruction device is not operated; and an automatically applied
parking brake force at the time of the parking brake operation
executed when the stop state is detected is set to a value smaller
than a normal parking brake force at the time of normal parking
brake operation by the operation of the parking brake operation
instruction device.
With this arrangement, since the control device controls the
electric parking brake system such that the parking brake force is
close to. and thus not very different from, the service brake force
used for stopping the vehicle, it is possible to minimize the
duration of the parking brake operation, so that the vehicle driver
does not feel a sense of discomfort. The parking brake operation by
the electric parking brake system thus can be used as a brake
assist application in more situations other than the normal parking
brake, and the application range can be expanded.
This control device may further include an automatically applied
braking force determination means that determines the automatically
applied parking brake force, in which the automatically applied
braking force determination means is configured to determine the
automatically applied parking brake force so as to be equal to the
braking force by the service brake estimated by the brake load
estimation means when the stop state of the vehicle is
detected.
By using the estimated value of the brake load estimation means so
that there will not be so large a difference between the braking
force by the service brake when the vehicle is brought to a stop
and the braking force of the automatically operated parking brake
operation, it is possible to more accurately set the automatically
applied parking brake force.
The brake load estimation means are only required to be capable of
detecting and estimating, by one of various methods, the brake load
acting between members on which a braking frictional force actually
acts due to the linear movement of the slide member, such as
between the brake disc and the brake pad. The brake load estimation
means may be means for detecting the distortion amount of e.g. the
caliper body when the brake is operated, means for detecting a
change amount of an electrical resistance between electrodes, means
for detecting a piston load by the brake with various types of
sensors, means for detecting a front-back force generated in the
vehicle (action torque corresponding to the movement in the front
and back direction of the vehicle) with a torque sensor, or the
like.
This control device may further comprise an inclination angle
detection means that detects an inclination angle of the vehicle in
a front and back direction of the vehicle while the vehicle is at a
stop, and a frictional force estimation means that estimates a
frictional force of the brake by the service brake while the
vehicle is at a stop; and the automatically applied braking force
determination means may be configured to calculate an estimated
value of a braking force necessary for maintaining the stop state
of the vehicle from the inclination angle obtained by the
inclination angle detection means and the frictional force obtained
by the frictional force estimation means, and determine the
automatically applied parking brake force from the estimated value.
The frictional force estimation means is only required to be
capable of detecting and estimating the frictional force
(frictional force acting on the contacting portion of the brake pad
and the disc, etc.) of the brake by the service brake at the time
of stopping, and, for example, may be similar in structure to the
brake load estimation means described above.
By calculating the estimated value of the brake force necessary for
maintaining the stop state of the vehicle based on the inclination
angle of the vehicle and the frictional force, it is possible to
reliably prevent the vehicle from going down a hill under gravity
against the will of the driver.
In each configuration described above, the control device may be
configured to stop the power supply to the electric motor when the
parking brake operation executed when the stop state of the vehicle
is detected is completed.
The vehicle is stopped by the parking brake operation at the time
of vehicle stop, so that the current flow to the electric motor for
operating the normal service brake does not need to be continued.
Therefore, the current flow is stopped after the parking brake
operation thus reducing the energy consumption.
In each configuration described above, the control device can adopt
a configuration of releasing the parking brake operation when a
pedaling force on a brake pedal becomes smaller than a threshold
value determined in advance. Alternatively, the control device can
adopt a configuration of releasing the parking brake operation when
a differential value of the pedaling force on the brake pedal
becomes smaller than a threshold value determined in advance.
According to such configuration, the parking brake is automatically
released when a reduction amount of the pedaling force of the
vehicle driver becomes greater than a threshold value, so that the
parking brake can be released without giving a sense of discomfort
to the vehicle driver.
If the brake release may possibly cause the vehicle to move
backward such as when starting on an uphill, the release of the
parking brake may be delayed to prevent such backward movement of
the vehicle.
In such configuration, the control device includes a driving force
detection means that detects a driving force acting on a drive
wheel of the vehicle; and the control device is configured to
calculate a necessary driving force necessary to prevent the
vehicle from at least not moving backward, from the inclination
angle obtained by the inclination angle detection means, the drive
force obtained by the drive force detection means, and the
information on the weight of the vehicle, when the vehicle is
inclined such that gravity acts on the vehicle in an opposite
direction with respect to the advancing direction of the vehicle,
and set a delay time for delaying the release of the parking brake
operation until the driving force reaches the above necessary
driving force.
The locking mechanism is only required to be capable of fixing the
slide member, which is configured to be moved linearly by the
rotation/linear movement converting mechanism, at a predetermined
position in the forward/backward movement direction, and may be
configured to directly make contact with the slide member to fix
the slide member or indirectly fix the slide member. For example,
the following electric parking brake system includes a locking
mechanism that indirectly fixes the slide member.
An electric parking brake system further comprising a gear
reduction mechanism provided between the electric motor and the
linear motion mechanism and configured to reduce the speed of, and
output, the rotation of the rotor shaft of the electric motor;
wherein the locking mechanism comprises a locking portion provided
on a side surface of one of a plurality of gears forming the gear
reduction mechanism, a locking pin configured to be moved forward
and backward with respect to the locking portion and brought into
engagement with the locking portion to lock the rotation of the
gears when the locking pin is moved forward, and a pin driving
actuator configured to move the locking pin forward and backward;
and the position of the slide member is fixed and the fixing is
released by the locking and unlocking of the gears by the locking
pin.
An electric brake system including the electric parking brake
system having one of the configurations described above may be
adopted, where the operation of the service brake by the operation
of the brake pedal is executed by the functions of the electric
motor, the rotation/linear movement converting mechanism, the
control device, and the brake load estimation means.
The brake system that uses the electric parking brake system having
each configuration described, and that can use the electric parking
brake system for the brake assist application even in the situation
of the service brake other than the normal parking brake can be
realized.
One electric parking brake system and electric brake system having
each configuration described above merely needs to be mounted on
one automobile, but two or more may be mounted. Furthermore, such
devices may be adopted for each brake of all the wheels.
In the present invention, the control device controls the electric
parking brake system so as to become a brake force close to the
service brake force used for stopping, that is, so that a great
variation does not occur in the brake force, whereby the operation
time of the parking brake becomes a minimum and the vehicle driver
does not feel a sense of discomfort. The parking brake operation by
the electric parking brake system thus can be used for the brake
assist application in more situations other than the normal parking
brake, and the application range can be expanded.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an explanatory view of an operation of an electric
parking brake system and an electric brake system according to one
embodiment of the present invention;
FIG. 2 is a system configuration diagram of the electric parking
brake system and the electric brake system;
FIG. 3 is a longitudinal sectional view of the electric parking
brake system and the electric brake system;
FIG. 4 is a sectional view showing in an enlarged manner a linear
motion mechanism and the brake system of FIG. 3;
FIG. 5 is a sectional view taken along line VII-VII of FIG. 3;
and
FIG. 6 is a sectional view of a linear solenoid.
MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be
described based on the drawings. This embodiment is directed to an
electric parking brake system that uses an electric linear motion
actuator A as a linear motion mechanism A for linearly driving
brake pads P with respect to a brake disc D, and an electric brake
system E equipped with the electric parking brake system.
As shown in FIGS. 3 and 4, the electric linear motion actuator A
and an electric motor M for actuating the electric linear motion
actuator A are arranged in parallel to each other. The rotation
force from the electric motor M is transmitted to the electric
linear motion actuator A by way of a gear reduction mechanism G,
and the electric linear motion actuator A presses the brake pads P
of the electric brake system E against the brake disc D to generate
a braking force.
In particular, the electric linear motion actuator A converts the
rotational movement of a rotor shaft 12 of the electric motor M to
a linear movement of a slide member 5, thus pressing the pads P
against the disc D to generate a braking force by the linear
movement of the slide member 5.
The electric linear motion actuator A is mounted in a cylindrical
housing 1. A base plate 3 extends radially outwardly from a first
end of the housing 1. The outer side surface of the base plate 3
and the opening of the housing 1 at the first end are covered with
a cover 4.
The slide member 5, in the form of an outer ring member 5, is
mounted in the housing 1. The outer ring member 5 is rotationally
fixed and is movable in the axial direction along the radially
inner surface of the housing 1. The outer ring member 5 has, on its
radially inner surface, a helical rib 6 having a V-shaped
section.
A bearing member 7 is mounted in the housing 1 at a first axial end
side of the outer ring member 5. Two rolling bearings 9 are mounted
in the bearing member 7 so as to be axially spaced apart from each
other. A rotation shaft 10 arranged on the axis of the outer ring
member 5 is rotatably supported by the rolling bearings 9.
As shown in FIG. 3, the electric motor M is supported by the base
plate 3 by way of a motor housing 11, and the rotation of the rotor
shaft 12 of the electric motor M is transmitted to the rotation
shaft 10 by the gear reduction mechanism G incorporated in the
cover 4.
A carrier 14 is mounted in the outer ring member 5 so as to be
rotatable about the rotation shaft 10. As shown in FIG. 4, the
carrier 14 includes a pair of discs 14a, 14b that face each other
in the axial direction. The disk 14a has, on the outer peripheral
portion of its side surface facing the disk 14b, a plurality of
interval adjusting members 14 which are circumferentially spaced
apart from each other and extend toward the other disc 14b. The
discs 14a, 14b are coupled to each other by tightening screws 15
screwed into the end faces of the interval adjusting members
14c.
Of the discs 14a and 14b, the inboard side disc positioned on the
side of the bearing member 7, namely the disc 14b, is rotatably and
axially movably supported by a slide bearing 16 incorporated
between the disc 14b and the rotation shaft 10. The outboard disc
14a is supported by a slide bearing 18 so as to be rotatable
relative to the rotation shaft 10.
The carrier 14 is provided with a plurality of circumferentially
spaced apart roller shafts 20 each having their ends supported by
the respective discs 14a, 14b. Each roller shaft 20 has its
respective end portions inserted in shaft inserting holes 21 in the
form of elongated holes formed in the respective discs 14a and 14b
so as to be movable in the radial direction. The roller shafts 20
are biased radially inwardly by two elastic rings 22 each wrapped
around the first or second ends of the roller shafts 20.
A planetary roller 23 is rotatably supported by each of the roller
shafts 20. The planetary rollers 23 are arranged between the
radially outer surface of the rotation shaft 10 and the radially
inner surface of the outer ring member 5, and are pressed against
(and thus brought into elastic contact with) the radially outer
surface of the rotation shaft 10 under the biasing force of the
elastic rings 22 wrapped around the shaft end portions of the
roller shafts 20. Thus, when the rotation shaft 10 is rotated, the
planetary rollers 23 are rotated due to frictional contact with the
radially outer surface of the rotation shaft 10.
As shown in FIG. 3, each of the planetary rollers 23 is formed, in
the radially outer surface thereof, with a plurality of axially
equidistantly spaced apart helical grooves 24 having a V-shaped
section. The pitch of the helical grooves 24 is equal to the pitch
of the helical rib 6 formed on the outer ring member 5, and the
helical rib 6 is engaged in the helical grooves 24. However,
instead of the helical grooves 24, each planetary roller 23 may be
formed with a plurality of axially equidistantly spaced apart
circumferential grooves, with the same pitch as the helical rib
6.
A washer 25 and a thrust bearing 26 are incorporated axially
between the inboard side disc 14b of the carrier 14 and each of the
planetary rollers 23. Furthermore, an annular thrust plate 27 is
disposed axially between the carrier 14 and the bearing member 7,
and a thrust bearing 28 is incorporated axially between the thrust
plate 27 and the bearing member 7. The opening of the outer ring
member 5 at the second end thereof, which is positioned outside of
the opening of the housing 1 at the second end thereof, is closed
by a seal cover 29 thus preventing entry of foreign substances.
Furthermore, a bellows 30 has one end portion thereof coupled to
the opening of the housing 1 at the second end, and the other end
portion thereof coupled to the second end portion of the outer ring
member 5, thereby preventing entry of foreign substances into the
housing 1.
As shown in FIG. 3, the gear reduction mechanism G transmits the
rotation of an input gear 31 attached to the rotor shaft 12 of the
electric motor M to an output gear 32 attached to the shaft end
portion of the rotation shaft 10, after sequentially reducing its
speed by means of primary to tertiary reduction gear trains G.sub.1
to G.sub.3, to rotate the rotation shat 10. The gear reduction
mechanism G includes a locking mechanism 40 that can lock and
unlock the rotor shaft 12 of the electric motor M.
The locking mechanism 40 has a plurality of locking holes (locking
portions) 41 formed in a side surface of an intermediate gear 33 on
the output side of the secondary reduction gear train G.sub.2 so as
to be arranged at equal intervals on a common circle. The locking
mechanism 40 further includes a locking pin 42 movable forward and
backward with respect to a point on the pitch circle of the locking
holes 41, and a linear solenoid 43 as a pin driving actuator S for
moving the locking pin 42 forward and backward, and is configured
such that when the locking pin 42 is engaged in one of the locking
holes 41 (as shown in FIGS. 5 and 6), the intermediate gear 33 is
locked in position.
In this embodiment, the locking portions 41 are holes that extend
through the intermediate gear 33, but the locking portions 41 are
not limited thereto. For example, the locking portions 41 may be
radial grooves defined between adjacent radial ribs formed on the
side surface of the intermediate gear 33. Alternatively, the
locking portions 41 may comprise recesses formed in the side
surface of the intermediate gear 33.
FIG. 4 shows a brake unit B using the electric linear motion
actuator A of the above-described embodiment. The brake unit B
includes a caliper body unit C integrally connected to the second
end of the housing 1 of the electric linear motion actuator A, and
a fixed brake pad P1 and a movable brake pad P2 disposed on the
front and back sides, respectively, of the outer peripheral portion
of the brake disc D that are located in the caliper body unit C.
The movable brake pad P2 is integrally coupled to the second end
portion of the outer ring member 5.
In this brake unit B, in which the electric linear motion actuator
A is used, when the electric motor M, shown in FIG. 5, is driven,
the rotation of the rotor shaft 12 of the electric motor M is
transmitted to the rotation shaft 10 after its speed has been
reduced by the gear reduction mechanism G.
Since the respective radially outer surfaces of the planetary
rollers 23 are in elastic contact with the radially outer surface
of the rotation shaft 10, when the rotation shaft 10 rotates, the
planetary rollers 23 rotate about their respective axes while
revolving around the rotation shaft 10, due to frictional contact
with the rotation shaft 10.
This causes the outer ring member 5 to be moved axially due to
engagement of the helical rib 6, which is formed on the radially
inner surface of the outer ring member 5, in the helical grooves 24
formed in the radially outer surfaces of the planetary rollers 23,
which in turn causes the movable brake pad P2, which is integrally
coupled to the outer ring member 5, to be pressed against the brake
disc D, thus applying a braking force to the brake disc D.
In parking the vehicle, the linear solenoid 43 is actuated to move
the locking pin 42 forward toward the side surface of the
intermediate gear 33, with the movable brake pad P2 pressed against
the brake disc D and a braking force necessary for parking applied
to the brake disc D, as described above.
If one of the plurality of locking holes 41 faces the locking pin
42 when the locking pin 42 is moved forward, the locking pin 42
engages in this locking hole 41 and the intermediate gear 33 is
locked by such engagement, as shown in FIGS. 5 and 6. At this time,
since the rotor shaft 12 of the electric motor M is also locked,
the electric motor M can be kept de-energized, so that it is
possible to reduce energy consumption.
If the locking pin 42 faces none of the locking holes 41 when the
locking pin 42 is moved forward, the locking pin 42 cannot be
engaged in any of the locking holes 41. In this case, the
intermediate gear 33 is rotated in the braking direction (direction
indicated by arrow A in FIG. 5) by driving the electric motor M
with the locking pin 42 moved forward, until the intermediate gear
33 is rotated to a position where one of the locking holes 41 faces
the locking pin 42 thus engaging the locking pin 42 in the locking
hole 41.
With the intermediate gear 33 and thus the rotor shaft 12 of the
electric motor M both locked in position due to engagement of the
locking pin 42 in one of the locking holes 41, rotation force in
the brake releasing direction is applied to the respective gears of
the gear reduction mechanism G by the reaction force from the brake
disc D, so that a rotation torque is applied to the engagement
portions of the locking hole 41 and the locking pin 42. Such
rotation torque is large at the position of the output gear 32 and
gradually becomes smaller toward the input gear 31.
In the embodiment, the locking holes 41 are formed in the side
surface of the intermediate gear 33, which is on the output side of
the secondary reduction gear train G.sub.2, so that rotation torque
applied to the engagement portions of the lock hole 41 and the
locking pin 42 is relatively small and the engagement portions of
the lock hole 41 and the locking pin 42 will not be damaged.
In order to more effectively prevent such damage, the locking holes
41 are preferably formed in the intermediate gear proximate to the
input gear 31. The position of the locking pin 42 is determined in
accordance with the positions of the locking holes 41.
As shown in FIG. 2, the electric brake system E includes a control
device 50 for controlling the electric motor M and the locking
mechanism 40. The control device 50 is controlled by an electronic
control unit (ECU) 55.
Furthermore, the electric brake system E includes a brake load
estimation means 60 that estimates the actually acting brake force,
and an electric parking brake operation instruction device 70 that
can be arbitrary operated by the will of the vehicle driver. When
the vehicle driver operates the electric parking brake operation
instruction device 70, the parking brake operation is carried
out.
The parking brake is applied when the locking pin 42 is engaged in
one of the locking holes 41, thereby preventing axial movement of
the outer ring member 5, and thus axially fixing the outer ring
member 5 in position, with a predetermined braking force being
exerted between the brake pad P and the brake disc D. Once the
parking brake is applied, the electric motor M is de-energized.
A normal parking brake force Fmax while normal parking brake is
applied by the operation of the parking brake operation instruction
device 70 is generally set to a value greater than a braking force
F.sub.0 of the service brake while the vehicle is at a stop. The
parking brake operation instruction device 70 generates the normal
parking brake force Fmax between the brake pad P and the brake disc
D by driving the electric motor M, before the outer ring member 5
is completely fixed in position by the locking mechanism 40.
FIG. 1(a) schematically shows the normal parking brake operation by
the operation of the parking brake operation instruction device 70.
In particular, the graph at the uppermost level of FIG. 1(a) shows
the relationship between the braking force F.sub.0 of the service
brake and the normal parking brake force Fmax; the graph at the
second level shows the pedal depressing force; the graph at the
third level shows the vehicle speed; the graph at the fourth level
shows on and off of the operation of the parking brake operation
instruction device 70; and the graph at the fifth level shows the
power consumption of the electric motor M. As shown, when the
parking brake is actuated, the brake pressing force is held by the
mechanical locking mechanism (locking mechanism 40), and the motor
power becomes zero, so that the brake pressing force basically does
not follow the pedal depressing force.
The control device 50 has a function of automatically executing the
parking brake operation when it is detected that the vehicle is at
a stop, even if the electric parking brake operation instruction
device 70 is not operated in this state. That the vehicle is at a
stop is detected through the speedometer and/or information on the
rotation of the drive wheels.
This automatic parking brake operation is also performed through
the engagement of the locking pin 42 and one of the locking holes
41 by the locking mechanism 40, with a predetermined braking force
necessary to stop the vehicle exerted between the brake pad P and
the brake disc D.
The automatically applied parking brake force F.sub.1 during
automatic parking brake operation is set to a value equal to or
substantially equal to the braking force F.sub.0 of the service
brake while the vehicle is at a stop. The control device 50
generates the automatically applied parking brake force F.sub.1
between the brake pad P and the brake disc D by driving the
electric motor M before the outer ring member 5 is completely fixed
in position by the locking mechanism 40.
FIG. 1(b) schematically shows the automatically performed parking
brake operation, which does not depend on the operation of the
parking brake operation instruction device 70. In particular, the
graph at the uppermost level of FIG. 1(b) shows the relationship
between the braking force F.sub.0 of the service brake and the
automatically applied parking brake force F.sub.1, which is equal
to the braking force F.sub.0; and similar to FIG. 1(a), the graphs
at the second to fifth levels of FIG. 1(b) show the pedal
depressing force, the vehicle speed, on and off of the operation of
the parking brake operation instruction device 70, and the power
consumption of the electric motor M, respectively.
In FIG. 1(b), the electric parking brake system is controlled to
generate braking force (automatically applied parking brake force
F.sub.1) equal to the braking force F.sub.0 when the vehicle is
brought to a stop (vehicle speed zero) after the vehicle driver has
applied brakes while the vehicle is traveling. While the parking
brake is applied, the power supply to the electric motor M is
stopped.
As can be understood from the comparison of FIG. 1(a) and FIG.
1(b), the automatically applied parking brake force F.sub.1 at the
time of the parking brake operation executed when the stop state of
the vehicle is detected is set to a value smaller than the normal
parking brake force Fmax at the time of the normal parking brake
operation by the operation of the parking brake operation
instruction device 70. The braking force F.sub.0 of the service
brake and the automatically applied parking brake force F.sub.1 are
set to be equal to or substantially equal to each other.
The control device 50 thus controls the electric parking brake
system so that there is no big difference between the braking force
of the service brake used to stop the vehicle and the braking force
applied during automatic parking brake operation.
As a result, it is possible to minimize the duration of the parking
brake operation, and the vehicle driver will not feel a sense of
discomfort. The parking brake operation by the electric parking
brake system thus can be used in a wider range of brake assist
applications other than the normal parking brake, and the
application range thereof can be expanded.
The automatically applied parking brake force F.sub.1 is set by the
control device 50. The control device 50 includes an automatically
applied braking force determination means 51 that determines the
automatically applied parking brake force F.sub.1. The
automatically applied braking force determination means 51 has a
function of determining the automatically applied parking brake
force F.sub.1 so as to be equal to the braking force F.sub.0 by the
service brake estimated by the brake load estimation means 60 when
the stop state of the vehicle is detected. The control device 50
carries out the parking brake operation based on such
determination.
An estimated value of the brake load estimation means 60 is adopted
so that a great variation does not occur between the braking force
F.sub.0 by the service when the vehicle is brought to a stop and
the automatically applied parking brake force F.sub.1 of the
parking brake operation automatically operated thereafter, so that
the automatically applied parking brake force can be more
accurately set.
The control device 50 further includes an inclination angle
detection means 52 that detects the inclination angle of the
vehicle in the front and back direction of the vehicle while the
vehicle is at a stop, and a frictional force estimation means 53
that estimates the frictional force between the friction pad and
the brake rotor by the service brake while the vehicle is at a
stop.
The automatically applied braking force determination means 51
calculates an estimated value of the brake force necessary for
maintaining the stop state of the vehicle based on the inclination
angle obtained by the inclination angle detection means 52 and the
frictional force obtained by the frictional force estimation means
53, and determines the automatically applied parking brake force
F.sub.1 from the estimated value.
By calculating the estimated value of the brake force necessary for
maintaining the stop state of the vehicle based on the inclination
angle of the vehicle and the frictional force, it is possible to
reliably prevent the vehicle from going down a slope under gravity
against the will of the driver.
Similar to the normal parking brake operation, the control device
50 stops the power supply to the electric motor M when the parking
brake operation automatically executed when the stop state of the
vehicle is detected is completed. In other words, once the parking
brake operation is complete, the electric motor M needs not to be
kept energized, and thus can be de-energized, thus reducing energy
consumption.
FIG. 1(c) schematically shows how the automatically executed
parking brake operation is released. The parking brake is released
when the value corresponding to the pedal depressing force becomes
smaller than or greater than a predetermined threshold value.
For example, the control device 50 may be configured to release the
parking brake operation when the absolute value of the pedal
depressing force becomes smaller than the predetermined threshold
value. Alternatively, the control device 50 may be configured to
release the parking brake operation when the differential value of
the pedal depressing force becomes smaller than the predetermined
threshold value.
The control device 50 may further include a driving force detection
means 54 that detects the driving force acting on the drive wheels
of the vehicle. In this case, the control device 50 is configured
to calculate a necessary drive force necessary to at least prevent
the vehicle from moving backward, from the inclination angle
obtained by the inclination angle detection means 52, the drive
force obtained by the drive force detection means 54, and the
information on the weight of the vehicle, when the vehicle is
inclined such that gravity acts on the vehicle in a direction
opposite to the advancing direction of the vehicle, and set a delay
time for delaying the release of the parking brake operation until
the driving force reaches the above necessary driving force. With
this arrangement, it is possible to prevent backward movement of
the vehicle during e.g. a hill start.
DESCRIPTION OF SYMBOLS
1 housing 5 outer ring member (slide member) 6 helical rib 10
rotation shaft 11 motor housing 12 rotor shaft 14 carrier 20 roller
shaft 23 planetary roller 31 input gear 32 output gear 33
intermediate gear 40 locking mechanism 41 locking hole (locking
portion) 42 locking pin 43 linear solenoid 50 control device 51
automatically applied brake force determination means 52
inclination angle detection means 53 frictional force estimation
means 54 driving force detection means 60 brake load estimation
means 70 electric parking brake operation instruction device A
electric linear motion actuator (linear motion mechanism) B brake
unit C caliper body unit D brake disc E electric brake system
(electric parking brake system) F.sub.1 automatically applied
parking brake force Fmax normal parking brake force G gear
reduction mechanism M electric motor P brake pad P1 fixed brake pad
P2 movable brake pad S pin driving actuator
* * * * *